For a storage system including a plurality of storage apparatuses, there is a data migration technique of migrating data from one storage apparatus to another storage apparatus. Data migration is executed by a controller module (a storage control unit) provided in a new storage apparatus (a storage apparatus of a data migration destination) in replacing storage apparatuses, for example.
For data migration, there is known a technique of continuing input/output (I/O, input and output of data) to and from a host computer (hereinafter referred to as “host”), counting the frequency of access to individual disks, and executing data migration preferentially from an area with high access frequency.
For a storage system, there is known a technique of evaluating the access states of sub-blocks obtained by dividing a logical unit number (LUN) by data migration unit and giving higher priority to data transfer of highly evaluated sub-blocks. Example related art documents include Japanese Laid-open Patent Publication No. 2000-187608 and Japanese Laid-open Patent Publication No. 2014-232348.